Process for the metathetic degradation of nitrile rubbers

Abstract

An improved process for the metathetic degradation of nitrile rubber using catalyst systems comprising the catalyst and also a phosphane or diphosphane is provided.

Description

FIELD OF THE INVENTION [0001] The invention relates to an improved process for the metathetic degradation of nitrile rubber in the presence of a catalyst and of a specific additive. BACKGROUND OF THE INVENTION [0002] The term nitrile rubber, also referred to as “NBR” for short, refers to rubbers which are copolymers or terpolymers of at least one α,β-unsaturated nitrile, at least one conjugated diene and, if desired, further copolymerizable monomers. [0003] Hydrogenated nitrile rubber, also referred to as “HNBR” for short, is produced by hydrogenation of nitrile rubber. Accordingly, the C═C double bonds of the copolymerized diene units are entirely or partly hydrogenated in HNBR. The degree of hydrogenation of the copolymerized diene units is usually in the range from 50 to 100%. [0004] Hydrogenated nitrile rubber is a specialty rubber which has very good heat resistance, excellent resistance to ozone and chemicals and excellent oil resistance. The abovementioned physical and chemic...

AI Technical Summary

Benefits of technology

[0021] It has now been found that the activity of metathesis catalysts in the degradation of nitrile rubbers can be increased by using them in combination with a phosphane or diphosphane. This is all the more surprising because a person skilled in the art would not have expected this on the basis of J. Am. Chem. Soc. 1997, 119, 3887-3897.

Problems solved by technology

The processability of HNBR is greatly restricted by the relatively high Mooney viscosity.

However, this thermomechanical degradation has the disadvantage that functional groups such as hydroxyl, keto, carboxylic acid and ester groups are incorporated into the molecule by partial oxidation and, in addition, the microstructure of the polymer is substantially altered.

The preparation of HNBR having low molar masses corresponding to a Mooney viscosity (ML 1+4 at 100° C.) in the range below 55 or a number average molecular weight of about Mn<200 000 g / mol was not possible by means of established production methods for a long time, since, firstly, a step increase in the Mooney viscosity occurs on hydrogenation of NBR and, secondly, the molar mass of the NBR feedstock to be used for the hydrogenation cannot be reduced at will, since otherwise work-up in the available industrial plants is no longer possible because of excessive stickiness.

However, the amounts of Grubbs (I) catalyst employed for carrying out the metathesis are large.

However, the amounts of ruthenium necessary for this efficient metathetic degradation are still relatively high and long reaction times are still required.

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